My two bed rented flat has old wall mounted electric heaters, see attached pic. I don't think they're storage heaters, just basic heaters. They're not great. The one in my small bedroom is mounted on an external wall, below a window. From an energy efficiency and cost effective standpoint does it make sense to just not use it, and buy an oil filled radiator instead, using it on the evenings and for an hour or so in the morning. Thoughts? Trying to cut down on the energy bills, but as a renter I don't have a lot of options.